SAN BRUNO — A federal grand jury is investigating at least one new instance of obstruction of justice against PG&E in connection with the deadly San Bruno blast, according to court papers filed in the criminal trial case.

The grand jury probe is separate from an existing allegation of obstruction that is one of the 13 charges PG&E is facing in the criminal case, according to court documents. While the existing obstruction charge says PG&E impeded the probe into the disaster by misleading federal officials, no further details were available about the new grand jury investigation.

“The government has disclosed . . . that a current, ongoing grand jury is investigating potential obstruction” against the utility, the documents filed by PG&E”s attorneys on March 3 said.

Word of the new grand jury prompted dismay from one of PG&E”s frequent critics.

“As more time passes, the more is being revealed about PG&E”s criminal behavior,” said state Sen. Jerry Hill, whose San Mateo County district includes San Bruno. “This is very troubling.”

In a separate development Monday, PG&E”s criminal trial stemming from the explosion will be delayed until at least April 12 — and probably later — U.S. District Court Judge Thelton Henderson ruled. Henderson conceded that an intensifying battle over documents being demanded by federal prosecutors and PG&E”s attorney will most likely require an additional delay.

Originally, the trial had been set to begin March 7.

Of the 13 criminal charges San Francisco-based PG&E faces in U.S. District Court, 12 are alleged violations of pipeline safety regulations and one is obstruction of an investigation into the explosion by the National Transportation Safety Board.

Also on Monday, PG&E said in court papers that it may not receive a fair trial because of publicity about the explosion, which killed eight and destroyed parts of a San Bruno residential area in September 2010.

“The steady drum beat of media coverage, which has vividly connected the tragic San Bruno explosion to this trial, appears to be reaching a crescendo at the most sensitive juncture, the eve of jury selection when such adverse publicity in the media may have the greatest prejudicial impact on the minds of potential jurors,” PG&E”s attorneys said in the court documents.

PG&E has pleaded not guilty to all the charges.

“Regardless of the next legal steps, we will remain focused on our mission of becoming the safest, most reliable gas company in the nation,” PG&E spokesman Gregory Snapper said.

At the hearing on Monday in San Francisco, government prosecutors and PG&E attorneys presented arguments in connection with the upcoming trial. At one point, the judge cleared the courtroom to discuss matters under seal.

If convicted, PG&E could face fines of up to $562 million in the criminal case. The original indictment in the matter was filed in April 2014.

The judge indicated during the court proceeding that his patience was wearing thin regarding the heated disputes over documents and witnesses for the trial.

“I”m not going to entertain any further motions on the discovery disputes,” he said. “Is that clear?”

In April 2015, the state Public Utilities Commission slapped PG&E with a $1.6 billion penalty to punish the company for its role in causing the blast. That levy was the largest penalty ever imposed on a U.S. utility company.

The explosion, according to federal investigators, was caused by a combination of PG&E”s shoddy maintenance and flawed record keeping, along with lazy oversight by state regulators. Ongoing investigations and hearings by the PUC could result in hundreds of millions of dollars in additional fines against PG&E.